The invention relates to an FM-broadcasting system incorporating an FM transmitter and an FM-receiver cooperating therewith, the transmitter signal comprising a multiplex signal which is frequency-modulated on a main carrier which multiplex signal comprises an audio-frequency information signal and, in the case of a stereo transmission, a stereo information signal modulated on a suppressed stereo subcarrier, as well as a stereo pilot whose frequency is situated between the frequency spectra of the two information signals and a binary, differentially coded code signal which is phase-modulated on a code subcarrier situated outside said frequency spectra.
The invention also relates to a receiver for use in such an FM-broadcasting system.
An FM-broadcasting system of the above-described type is known from Netherlands Patent Application No. 7800581which has been laid open to public inspection. In this known FM broadcasting system binary information is transmitted with the aid of the code signal for an easily recognizable transmitter identification. This transmitter identification may consist of an identification of the FM-transmitter to which the tuner is tuned and/or the program transmitted by the transmitter.
The receiver for this known FM-broadcasting system comprises a code signal demodulator for a phase-demodulation of the modulated code signal and a decoding circuit connected thereto which decodes the binary signal and employs it usefully, for example for a full or partial optical display of the transmitted binary information. The use of a differential code for the binary transmitter identification information to be transmitted then eliminates the phase duplicity caused during the demodulation procedure.
As is known, during the decoding of a binary differentially coded signal, such as the code signal, a comparison takes place of the instantaneous value of the binary signal with the value the binary signal had one bit repetition period prior thereto. In order to enable such a signal comparison, the decoding circuit of the said receiver must delay the code signal for exactly one bit repetition period. In the case of deviations in said delay time, for example due to temperature variations, ageing etc. faulty decodings occur, which manifest themselves in a faulty display of the transmitted transmitter identification information.